Tavatanakit led the first LPGA major of the year from the first round, with the 21-year-old seeking to complete a remarkable debut victory at the Mission Hills Country Club in California.

The Thai, who made her professional debut last year, held a five shot lead heading into the final round.

New Zealand's Ko enjoyed a stunning start to the last day to close the gap to the leader, recording seven birdies and one eagle during the first 11 holes.

Ko achieved one further birdie on the back nine to finish with a round of 62, which matched Lorena Ochoa's record for the lowest round at the tournament.

The effort would only prove enough for second place overall, as a four-under-par final round of 68 saw Tavatanakit remain clear.

Tavatanakit finished the tournament 18-under-par, one shot shy of the Dottie Pepper record of 19-under, which was set in 1999.

She finished two shots clear of Ko to secure victory.

The debutante becomes the first rookie to win the event since the United States' Juli Inkster, who triumphed on debut in 1984.

Tavatanakit said she had been unaware of Ko's surge as she tried to seal victory.

"I didn't really look at the leaderboard," Tavatanakit said.

"I didn't really care who did anything, I just wanted to focus on myself.

"It still hasn't really sunk in yet the fact that I just turned 21 six months ago and now I'm a major champion in my rookie year."

South Korea's Sei Young Kim was part of a four-way tie for third place, as she finished on 11-under-par alongside the United States' Nelly Korda, Denmark's Nanna Koerstz Madsen and China's Shanshan Feng.